B727 FLT CREW HAS CONCERNS WITH LNDG PERFORMANCE FIGURES FOR CYMX.

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APPROX 30 MINS INTO FLT; A FLT CREW MEMBER RAISED THE QUESTION OF A CUTBACK CALCULATION FOR RWY 6 AT OUR DEST. RWY 6 LISTED IN THE DEP PAPERS AN LDA OF 9000 FT ON AN ORIGINALLY 12000 FT RWY. THE NORMAL RWY LNDG LIMIT WT IS 170000 LBS. THE AOM LISTS A CUTBACK FACTOR OF 39 LBS PER FT. THIS YIELDS A CUTBACK PENALTY OF 117000 LBS. THIS MAKES THE LANDABLE RWY LIMIT OF 530000 LBS. WE ACARS'ED FLT CTL STATING; 'RWY 6 NOTAMED LDA OF 9000 FT. PLEASE CALCULATE NEW RWY LNDG LIMIT WT.' AFTER 20 MINS WE RECEIVED NO RESPONSE. WE CONTACTED FLT CTL AND ASKED IF THEY RECEIVED OUR ACARS MESSAGE. FLT CTL SAID 'WE'RE WORKING ON IT.' THEN FLT CTLR SENT AN ACARS MESSAGE: 'FROM AOM; 5400 FT REQUIRED FOR LNDG AT YOUR ESTIMATED LNDG WT/FLT CTLR.' WE REJECTED THE ACARS MESSAGE AND RESENT THE ORIGINAL WORDING OF THE FIRST ACARS MESSAGE TO FLT CTLR. FLT CTLR'S WORDING DID NOT SATISFY US THAT THE RWY LNDG LIMIT WT HAD BEEN CALCULATED AND WAS LEGAL. HOWEVER; I DECIDED THE SAFEST AND MOST REASONABLE COURSE OF ACTION WAS TO LAND AS PLANNED ON RWY 6 RATHER THAN HOLD OR DIVERT. I POLLED THE CREW TO SEE IF THEY CONCURRED. THEN FLT CTLR SENT A SECOND MESSAGE STATING; 'GOOD TO STRUCTURAL 142500 LBS. DO YOU CONCUR?/FLT CTLR.' THIS STILL DID NOT MENTION 'RWY LNDG LIMIT WT.' AS A CREW WE AGREED THAT THEY WERE BEING ELUSIVE WITH THEIR WORDING. I AGAIN STATED MY INTENTION TO CONTINUE TO LNDG AND ASKED THE CREW IF THEY WERE OK WITH THAT. THE CREW AGREED. LNDG WAS UNEVENTFUL. AS CREW MEMBERS; WE SHOULD HAVE POSED THE QUESTION OF LEGAL PERFORMANCE LIMITS WHEN SEEING THE RWY LDA 9000 FT NOTAM IN THE DEP PAPERS. THE NEW DATA SHEET LNDG LIMITS SHOULD HAVE BEEN INCLUDED IN THE DEP PAPERWORK.